[en] Highlights: ► We investigated electronic structure and impurity states of different S-doping levels in cBN crystal theoretically using LDA approach in the frame of DFT. ► Both theory and experiment indicate that S is more likely to be substituted for a B atom than an N atom. ► S substituted for an N atom creates shallow electron levels merged to the states at the conduction band edge, and S substituted for a B atom creates deep levels within the band gap, both forming n-type cBN. - Abstract: The electronic structure and impurity states of S-doped cBN were investigated by first-principle approaches. Our calculation shows that S substituted for an N atom creates shallow donor levels merged to the states at the conduction band edge, S substituted for a B atom creates deep donor levels within the band gap, both forming n-type cBN, and band gap of S-doped cBN decreases with the increase of dopant concentration. Moreover, from the view of energy, S is more likely to be substituted for a B atom than an N atom.